The buses, vans and pickups from Thailand’s north and northeast packed with pro-government red shirts, trickled in all Saturday at the rally site on the western edge of Bangkok.

Their message, according to leaders, was to warn off anti-government protesters and independent agencies they see as conspiring to force caretaker prime minister Yingluck Shinawatra whom they powered to an election victory in 2012, out of office.

The same day, rhetoric rose to fever pitch, with anti-government protest movement leader Suthep Thaugsuban pledging to seize power and propose a new prime minister to the King.

Foreign Minister Surapong Tovichakchaikul told reporters: “If the prime minister is removed from her position, a power vacuum will occur and chaos will definitely ensue. Thais are hot-tempered and a confrontation could take place.”

Earlier on Friday, the Peua Thai party appeared to virtually draw a line, with legal advisor Bhokin Bhalakula telling a press conference the constitutional court may be within its jurisdiction in censuring the prime minister, but it should not go so far as to name a replacement premier.

If it did so, the court would be “tearing up the constitution” and “the people” would not accept that, he warned.

Thailand's ruling party is barely clinging to power after dissolving parliament last December and running an election on February 2 which was sabotaged by anti-government protesters and subsequently annulled by the courts, leaving the country in a grinding limbo now well into its fifth month, with no sitting parliament or imminent election.

By late Saturday evening, the number of “red shirts” at the rally seemed well short of the 500,000 organisers hope will turn up. The rally is scheduled to last through the weekend though.

The mood was festive of course. But it was the first time in months that the red shirts have staged a rally in Bangkok – albeit far from the downtown encampment of the People’s Democratic Reform Committee (PDRC) which wants to “eradicate” the influence of the premier’s billionaire brother Thaksin Shinawatra from Thailand, seeing him as a corrupt authoritarian seducing upcountry masses with money and promises and bent on supplanting the power of the monarchy itself.

The rally was called by the United Front for Democracy Against Dictatorship (UDD), an umbrella group for the red shirt movement.

Leader Jatuporn Promphan, who himself faces charges related to his role in protests in 2010 that turned violent and bloody, told The Straits Times it was inevitable that Yingluck would be forced out of office by either of two independent organisations: the National Counter Corruption Commission or the Constitutional Court both of which are hearing charges against her.

“This rally is a message to the people backing the PDRC to use democratic means, else the net result will be a civil war which nobody wants because of the social and economic cost,” Jatuporn said.

“The UDD is sending a message not to the television set but to the people who are holding the remote control. We know the independent organisations are not independent, that’s why we are here.”

The UDD believes the independent organisations are merely arms of the elite establishment bent on wiping out Thaksin’s network.

But the red shirt rally was not the most significant development on Saturday. PDRC leader Suthep Thaugsuban told supporters to get ready for a “final battle” and added: “When the day comes, we will seize the ruling power immediately.”

Local media quoted him saying: “Our words will be law. We will seize the assets of the Shinawatra family members. They will need to report to us. We will appoint the prime minister of the people and submit the name to His Majesty, to be countersigned by me. After that, we'll set up the People's Council, which will lead reform before the country can proceed with a fresh election.”

He said all this would be done after the Songkran water festival and the final push would take about 15 days.

At the red shirt rally, Jatuporn also predicted the crisis would come to a head after Songkran which runs from April 13-16, with court rulings forcing Yingluck to step down. This weekend rally was a “rehearsal” for the mobilisation of the red shirts after that, he said.

One of the red shirts’ ideologues, former human rights commissioner and political science professor Jaran Ditta-apichai, told The Straits Times while the current crisis may be resolved, the longer struggle pitting the red shirts claiming to fight for democracy, against the royalist establishment elites, would continue for years.

The power struggle is being waged against the backdrop of an increasingly frail King Bhumibol Adulyadej, who turned 86 last December. Mostly in private – because there is a strict law forbidding criticism of the monarchy – Thais worry over a future without his over six decades of steadying influence. There is also acute – but again only privately voiced - anxiety over the possibility of a contested succession.

Thus far, the Crown Prince who is the official heir to the throne, has not made any overt political comments or gestures aside from a call for restraint very early in the five-month crisis.

But some red shirts supporters on Saturday wore T shirts for the first time printed with the words “We love the Crown Prince”. It was a change from previous gatherings after the bloody summer of 2010, when anti-monarchy graffiti was scrawled by red shirts in downtown Bangkok.

The UDD’s rally site is next to one of Crown Prince Maha Vajiralongkorn’s palaces. UDD leaders claimed this was a coincidence. But some supporters at the rally reportedly claimed the Crown Prince was on their side – something impossible to verify. Thailand's monarchy is at least on paper, above politics.

To be sure, the government’s days seem numbered.

Though some party insiders say if the constitution court rules that Yingluck acted without justification in transferring the previous head of the National Security Council Thawil Pliensiri in 2001 – and forced Yingluck and the entire Cabinet to step down - the order would only apply to the Cabinet that passed the decision at the time.

Those inducted into the Cabinet after that would still be in place, and could appoint an acting premier.

But Yingluck’s removal by one of the agencies involved – most probably the constitutional court – could be the trigger regardless, for the “chaos” Surapong and others have warned of.